The object of the invention in accordance with the parent application Ser. No. 940,761 is to create a circuit for controlling a brushless electric motor that allows the motor to run slowly independent of the line frequency.
This object is attained by the invention in accordance with the parent application in that the line voltage is supplied to the stator winding through a phase-control circuit and the polarity of the voltage supplied to the coil is always changed subsequent to a number of line periods.
This solution means that the frequency of the resulting rotary field can be essentially lower than the line frequency, allowing the motor to run more slowly than in the case of synchronous operation. The motor can then for example be employed in a washing machine to directly drive the drum in both rapid and slow operation.
The maximum motor speed is dictated by the line frequency, amounting to 3000 rpm in a single-pole embodiment for example. A higher speed is not directly possible with the circuitry in accordance with the parent application.
In practice, however, motors with a higher speed, 6000 to 9000 rpm for example, are often necessary.